1. Field of Invention
The present invention relates to an electrical contact, more particularly, to an electrical contact having good fusing resistance, good abrasion resistance and low contact resistance.
2. Related Prior Art
An electrical contact is an important component used in various switches in daily life. The selection of materials of the electrical contact is critical as it has direct influence on the electrical life and reliability of the switch having the electrical contact. The following are common materials of the electrical contact currently used in the market.
AgCdO has good temperature rising property, and is both abrasion resistant and fusing resistant, but Cadmium therein is a toxic material which has now been replaced by other environmental protective contact materials.
AgSnO2 has good fusing resistance. However, it has high contact resistance and therefore is hard to be produced.
AgZnO has advantages of short arc time and high thermal stability under medium-low loading condition, but the extensibility and formability thereof is poor and hard to be produced.
AgW has good fusing resistance, but has problem of high contact resistance under non-protective atmosphere.
AgNi is applied to low-voltage switch and has advantages of low contact resistance and easily welded, but fusing resistance ability thereof is poor.
AgFe has advantageous characteristics as good arc-proof and fusing resistance, but AgFe will form iron oxide under high temperature and the iron oxide will deposit on surface thereof and results in a sudden deterioration of the temperature rise, thus the operation of the switch used an electrical contact made of AgFe will be affected.
Stainless steel is an alloy of chromium and nickel materials such that an electrical contact made by the stainless steel has advantages of good corrosion resistance and good wear resistance. However, compare to an electrical contact including silver-based material, the stainless steel electrical contact has the disadvantage of high contact resistance.
An electrical contact having multi-layer structure is disclosed in U.S. Pat. No. 7,015,406. The electrical contact has a main body made of copper or stainless steel, a middle layer made of silver or nickel and disposed on the main body, and a contact layer made of platinum group metal and disposed on the middle layer.
Another electrical contact is disclosed in Japan Pat. 2007-138237A. The electrical contact includes a stainless steel body having a surface which is coated with a silver layer by electroplating process. In more detail, before electroplating the silver layer to the stainless steel body, the stainless steel body must be previously coated a nickel layer with thickness from 0.01 to 0.1 μm and a copper or copper alloy layer with thickness from 0.05 to 0.2 μm, and then subjected the two layers to activation treatment in order to improve the bonding strength between the stainless steel body and the silver surface layer. However, the stainless steel body still has problems of poor processability and high contact resistance, and not suitable to be applied to a switch under low or middle loading conditions.